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Understanding the Causes of Hydrologic Changes in the Eurasian Arctic

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Title: Understanding the Causes of Hydrologic Changes in the Eurasian Arctic


1
Understanding the Causes of Hydrologic Changes in
the Eurasian Arctic
  • UBC/UW Hydrology Conference
  • September 29, 2006
  • Jennifer Adam
  • Dennis Lettenmaier
  • Department of Civil and Environmental Engineering
  • University of Washington

2
Study Domain Eurasian Arctic
Indigirka
Lena
Yenisey
Ob
Severnaya Dvina
-18 -12 -6 0
6
Mean Annual Air Temperature, ?C
3
Observed Streamflow Trends
  • Discharge to Arctic Ocean from six largest
    Eurasian rivers is increasing, 1936 to 1998
    128 km3/yr (7 increase)
  • Most significant trends during the winter
    (low-flow) season

Winter Trend, Ob
Bowling et al. 2002
4
Importance of Arctic Climate Studies
  • Largest warming observed in Arctic regions

1
Jones et al. 1999
5
Importance of Arctic Climate Studies
  • Arctic regions sensitive to change many changes
    observed already

2
  • Hydrological sensitivity to small changes in
    temperature, especially when and where
    temperatures are near threshold 0 C
  • Currently experiencing system-wide change
    rivers, permafrost, snow, glaciers, wetlands,
    vegetation zonation, fire frequency

6
Importance of Arctic Climate Studies
Potential for feedback response to global climate
3
Global Thermohaline Circulation
7
Importance of Arctic Climate Studies
  • Low level of understanding

4
  • How Arctic land surface hydrology will respond to
    predicted climate changes
  • How elements of the cryosphere (e.g. permafrost)
    modulate these interactions
  • How Arctic hydrological changes may provide a
    feedback response to global climate

8
Research Question
  • To what extent can long-term trends in Eurasian
    Arctic streamflow be explained by changes in
    precipitation and what are the most likely
    explanations for discrepancies between streamflow
    and precipitation trends, e.g. reservoir
    construction, changes in evapotranspiration (ET),
    and/or changes in soil moisture dynamics (such as
    permafrost degradation)?

9
Streamflow Trend Attribution
  • Water Balance
  • Hypothesized contributors
  • Acceleration of the hydrologic cycle P , ET?
  • Permafrost Degradation dS/dt , ET?
  • Reservoir Operation dS/dt?, ET?
  • Other fires, land use, wetlands, clouds,

Storage,S ground water/ice, lakes, surface ice
10
Status of Current Research
  • McClelland et al. (JGR, 2004)
  • Berezovskaya et al. (GRL, 2004)
  • Pavelsky and Smith (JGR, in review)
  • New contributions from our work
  • Seasonality taken into account
  • Multiple periods
  • Defined a set of most likely primary controls
    (most to least important) for a range of basins
    across the domain

11
Major Reservoirs (Capacitygt1 km3)
  • Lena 1
  • Yenisey 8
  • Ob 3

McClelland et al. 2004
12
Frozen Ground and Hydrology
  • Key features of frozen ground
  • permafrost vs. seasonally frozen ground
    permafrost is perennially frozen hydrologic
    activity is constrained to the warm season active
    (thawed) layer in permafrost
  • impermeable boundary frozen groundwater is
    hydrologically inactive and limits infiltration,
    although conduits can exist in non-continuous
    permafrost types baseflow generation is affected
  • excess ground ice beyond what unfrozen soil can
    hold mainly in top 10 m of permafrost inherent
    uncertainty

13
Permafrost Distribution (Brown et al. 1998)
Lena 100 permafrost (all types)
Yenisey 89 permafrost (all types)
Ob 26 permafrost (all types)
14
Hypothesis Formulation
Correlation Analysis Annual Basin Mean Air
Temperature vs. Annual Streamflow e.g. Ob ?-0.4
?
15
Trend Analysis
  • Selection of trend test
  • Sensitive to seasonal differences in trend
  • Varying periods between 1936 and 2000 (400)
  • Test for 99 significance
  • Calculate trends for precipitation, temperature,
    and streamflow (gauged and reconstructed)

16
Temperature Precipitation Trends, 99
Significant
Lena
Yeni.
Ob
  • Secondary basins are in order from coldest to
    warmest

Secondary Basins
Prcp. mm/year2
Temp. ?C/year
17
Streamflow Trends, 99
Ob
Lena
Indigirka
Aldan (Lena)
Lena (head)
Ob (head)
Yenisey
S. Dvina
Q, mm/year2
18
Precipitation Trends (streamflow periods 99)
Ob
Lena
Indigirka
Aldan (Lena)
Lena (head)
Ob (head)
Yenisey
S. Dvina
Prcp. mm/year2
19
Stream Flow/Precipitation Trends
Gauged
Recon.
Stream Flow Trend, mm/yr2
Gauged
Precipitation Trend, mm/yr2
20
Example Lena
Gauged (with reservoir)
Reconstructed (without reservoir)
21
Example Yenisey
4
Gauged (with reservoir)
2
0
Stream Flow Trend, mm/yr
0 2 4
2
3. Is this line tilted away from the one-to-one
line? NA
Reconstructed (without reservoir)
0
0 2
Precipitation Trend, mm/yr
22
Summary of Controls
23
Final Remarks
  • Warm basins Precipitation coupled with ET
    effects are major contributors reservoirs play a
    role for regulated basins.
  • Permafrost basins complex interactions among
    contributors
  • Threshold basins difficult to predict which
    basins most influenced by permafrost
  • Ground ice is the main complicating factor in
    understanding long-term streamflow changes
  • Modeling study concurrently being applied (e.g.,
    to explore the role of ground ice as a linkage
    between climate and streamflow changes)

24
Questions?
25
Stream Flow/Precipitation Trends
Gauged
Recon.
Stream Flow Trend, mm/yr2
Gauged
Precipitation Trend, mm/yr2
26
Reservoirs
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